This invention relates to mounts for optical components such as folding or periscope prisms, and more particularly to an improved mounting assembly for such components.
Prisms, or their equivalents assembled from coated mirrors, are often used in both conventional optics and laser systems. In particular, folding and periscope prisms or optics serve the functions of providing beam translation in space, with nominal 180.degree. and 0.degree. directional reversal respectively. In general, this is accomplished with reflecting surfaces which are orthogonally aligned (a folding prism) or parallel to each other (a periscope prism). In the case of the folding devices, the 45.degree. reflective surfaces provide retroreflection of the beam, when viewed from the side, but only in the plane perpendicular to the 90.degree. faces. In the case of periscopes, the parallel reflecting faces ensure that the output beam is undeviated in angle from the input beam. In most applications, these prisms are employed to take advantage of the stability of the output beam axis orientation against minor perturbations of the input, caused by thermal changes in the structure, etc. Accordingly, the mounts for such devices are generally fabricated to be simple and rigid. The optical elements are simply bonded in place prior to insertion into an optics system, using a fixture which simulates the precision tolerances to which the remainder of the system is fabricated.
The complexity of modern laser systems is extreme, however, particularly when several laser devices must be mounted on a single optical bench or structure. In particular, it may be impractical to establish the positions and angles of the components in the input and exit optical beam lines to the fine precisions (e.g., 10's of microradians in angle or 100's of microns in position) required using solely the adjustment of mechanical tolerances of the components. Such systems do not allow the use of off-line bonding or pre-alignment fixtures, but rather require that adjustments be made after the equipment is assembled.
Because of the shape of periscope and folding optical devices and because they have no mounting points to which attachment/adjustment mechanisms can be readily affixed, provision of in-situ adjustments has been clumsy in the past. An alternative method which has been employed in the past is to position the prisms to nominal values, and utilize separate optical elements (i.e., rotating Risley prism pairs) to adjust beam angle and position. This is undesirable, because of the additional cost, volume, weight, attenuation, and unreliability which inheres in adding such complexity. Another approach has been to replace the monolithic periscope or folding prism structure with one or more adjustable mirror mounts oriented to provide the periscope or fold structures with some in-place adjustability. This approach is also undesirable because the conventional mount designs which are used are invariably large, expensive, and introduce the danger of long-term instability due either to design or assembly defects.
This invention is directed to an optical mounting assembly that overcomes these disadvantages.